1. Field of the Invention
The present invention relates to an apparatus and a method for determining whether or not acoustic feedback is occurring in a sound-signal system in which a microphone and a speaker are connected.
2. Description of the Related Art
In a sound-signal system in which a microphone and a speaker are connected, part of an output from the speaker is fed back to the microphone, which may cause the so-called acoustic feedback (which is an oscillation phenomenon). The acoustic feedback often produces annoying middle/high frequency regular noise, such as squealing noise, and also may produce low-frequency regular noise, such as booming sound.
Acoustic feedback occurs not only in acoustic equipment (various public address systems) in which a microphone and a speaker are connected but also in headphone systems and hearing aids equipped with noise canceling systems.
Thus, various technologies for acoustic feedback have been developed. For example, Japanese Unexamined Patent Application Publication No. 08-193876 discloses an apparatus and a method that perform FFT (Fast Fourier Transform) processing on sound signals collected by a microphone, that determine a peak frequency point of power spectra, and that determine whether or not acoustic feedback is occurring.
Japanese Unexamined Patent Application Publication No. 2004-032387 discloses an apparatus that measures a time in which acoustic feedback is occurring and a time in which no acoustic feedback is occurring, that sets a gain upper limit of sound signals in accordance with the length of the measured time, and that controls the gain of the sound signals so as to prevent acoustic feedback.